The present invention relates to luminaires or street lights and, more particularly, to a shield for protecting the lens and light source thereof.
Typically a luminaire or street light includes an open-bottom housing for a light source and a lens-bearing door movably mounted on the housing for closing the bottom thereof and for mounting a lens below the light source. The housing includes a socket for the lamp source. The lens may be light-diffusing or simply a clear lens disposed so as to protect the light source. The lens is mounted on a door which is pivotally secured to the housing and movable between a raised orientation for protecting the light source and a lowered orientation enabling access to the light source--for example, for replacement thereof. While the lens provided in the door is typically adequate to protect the light source against unintended accidental impacts from projectiles, it has not been found adequate to protect the light source against vandals who are intentionally attacking the luminaire, frequently with guns ranging from the homemade pistol to an assault rifle.
U.S. Pat. No. 4,460,945 discloses a luminaire shield formed of a transparent laminate, commercially known as LEXGARD and formed of two polycarbonate sheets (commercially available under the mark LEXAN) with acrylic material therebetween. The laminate is about 0.75 inch thick, and the shield is spaced from the luminaire by spacer elements for ventilation purposes.
The laminate shield described above has not proven to be satisfactory in use. The laminate duly performs its function of protecting the light source from damage due to the impact of many projectiles (including pistol bullets) which cannot penetrate the laminate. However, such projectiles may at least partially delaminate the laminate, thereby reducing the light transmissiveness of the laminate due to the irregular refractive air space formed by the delamination. The degree of delamination appear to increase over time after the initial impact, so that the loss of light transmission is progressive. Inasmuch as eventually the luminaire does not provide adequate illumination through the delaminated laminate, the shield must be replaced, thus requiring both a costly service call and a costly new shield.
Another approach taken by the vandals has been to attack the connection between the shield and the luminaire. This has included both the direct approach of attempting to shoot out any means structurally connecting the shield to the luminaire and the indirect approach of simply repeatedly impacting the shield with projectiles so that the resultant vibrations cause the connected elements to separate. In either case, once the shield is gone from the luminaire, the luminaire is susceptible to conventional attack.
Further complicating the situation is the fact that the shields are often difficult to properly mount onto the luminaire, thereby increasing the time and thus the cost of a shield replacement.
Accordingly, it is an object of the present invention to provide a shield for a luminaire which will stop projectiles (including bullets) from piercing the shield and damaging the light source.
Another object is to provide such a shield which will not shatter, delaminate or otherwise undergo a substantial reduction of light transmissiveness as the result thereof.
A further object is to provide such a shield which offers protection to the means connecting the shield to the luminaire and which resists disengagement of the connected elements due to vibration.
It is also an object of the present invention to provide such a shield which may be easily and rapidly mounted and/or replaced on a luminaire.